In general, a liquid crystal panel is constituted by putting a back substrate provided with a thin film transistor, a pixel electrode and an alignment layer, and a front substrate provided with a color filter, an electrode and an alignment layer opposite each other, and injecting a liquid crystal between both substrates. For the purpose of bonding two substrates, a sealant is used.
At present, a heat-curable sealant containing an epoxy-based heat-curable resin as a main component is mainly used as the sealant, and it requires about 30 minutes or more until curing is completed and thus there is sometimes shift in the lateral direction of two preliminarily positioned substrates. In a sealing method such as an ODF method (One-Drop Filling method: liquid crystal drop method) in which a liquid crystal is directly contacted with an uncured sealant, there arises a problem that the uncured sealant component is dissolved in the liquid crystal between until curing is completed and thus the voltage-holding ratio of the resulting liquid crystal panel decreases.
Therefore, there have recently been increasing requirements for a photocurable sealant which is quickly cured and also can be used in an ODF method.
A cation-curable sealant and a radical-curable sealant are known as photocurable sealants. In general, the cation-curable sealant easily satisfies both excellent adhesion and excellent moisture barrier properties. However, there arose a problem that ionic compounds generating from a photocationic initiator with light irradiation dissolve in liquid crystals and cause contamination. In contrast, the radical polymerizable sealant does not generate ionic compounds and therefore causes less contamination to liquid crystals. However, there arose a problem that it is difficult to satisfy both high adhesion and low moisture permeability. There is known a photocurable composition for a sealant in which a maleimide having a condensed-type alicyclic structure such as a dicyclodecane structure, an adamantane ring or a tricyclodecane ring is used (for example, refer to Patent Document 1). The sealant has an alicyclic structure and is therefore excellent in moisture barrier properties. However, the sealant does not sufficiently satisfy adhesion required in the case of aiming at a more solid liquid crystal panel (for example, adhesion of 6 MPa or more is recently required).
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2005-171135